The invention relates to a method for measuring the mass and/or moisture of the contents of capsules, containing, in particular, medicinal products, pharmaceutical products, vitamins and similar products, with the aid of microwaves, in which method the displacement of the resonant frequency and broadening of the resonance curve caused by the capsules in a resonator is determined and evaluated, and to an apparatus for carrying out the method.
Such a method can be used to determine the mass and/or moisture of portioned active ingredient units, in particular also capsules (EP 1 467 191 A1). If the weight of the capsule casing is known, by establishing the difference the mass of the contents of the capsule, which contains, in particular, medicinal products, pharmaceutical products, vitamins or similar products, is obtained. If, however, the mass of the contents of the capsule is substantially less than the mass of the capsule casing, non-uniform masses of the capsule casings lead to considerable errors when determining the mass of the contents. An exemplary capsule has a mass of 50 mg, while the mass of the capsule contents, comprising carrier material and active ingredient, is 5 mg. This typical example alone shows that, if the capsule mass varies by +/−5 mg, a measurement of the mass of the contents on ready filled capsules is no longer possible, even if the overall accuracy of the measurement is less than 0.5 mg. It is particularly important, however, especially with small amounts of ingredients and active ingredients, to know the amount contained in the capsule. For this purpose, the capsule could, for example, be weighed before and after filling. However, apart from the fact that this necessitates intervention in the filling machine, the mechanical operation of weighing always requires a certain amount of time, so that many balances would have to be arranged parallel to one another to obtain a sufficiently high throughput. A further example involves the measurement of the total mass of the empty and filled capsule in the region of the filling machine by two appropriately arranged microwave measuring systems (EP 1467191 A1).